Color synchronizing apparatus



April 17, 1962 A. c. scHRoEDr-:R

' CQLQR SYNCHRONIZING APPARATUS voriginal Filed Jan. 5, 1952v 2 sheets-sheet 1 4 SEE 'I COLOR SYNCHRONZING APPARATUS l original Filed Jan.. 5, 1952 2 sheets-sheet z Alfred C. Schroeder,

Continuation of application Ser.

quency that are injected v oscillator in the receiver with the received lsi'gnal.

some of the previously suggested synchronizing arrange- -the normal operating ray devices 5, 6 and each of the selected component colors.

known type.

The p resent invention relates to apparatus for syn-4 chronizing an oscillator in a receiver with a series of recurrent bursts of alternating current energy having a desired phaseA and frequency. This application is a continuation of my patent application, Serial No. 265,084, filed JanuaryS, 1952, now abandoned.

A color television system has been proposed in which the color information is carried by a subcarrier' having a h ue andan amplitude representing In order to detect the phase of the subcarrier at a receiver and hence determine the hue phase representing chroma or saturation.

to be reproduced in the color image, it is necessary to United safes.Y Patent O I band of video signals are providea source of waves having a standard or knownv Generally this source takes the form of an oscillator and various means have been suggested for synchronizing this oscillator with bursts of standard freintothe normal television signal.

In these receivers signals are provided to different color channels by modulating differently phased outputs of-the phase.

ments the circuits have employed separate phase comparison devices which may have'inherent errors..

Therefore, the object of the present invention is to proi videan improved means for synchronizing an oscillator Vthe output of the oscillatorl of a color receiver in which 'is applied lto means for detectmg the phase of an incoming subcarrier wherein the synchronizing arrangement includes circuits of the receiver and minimizes the addition of separate circuits that may induce inherent errors. v i

The manner in which this objective may be attained may be briefiy set forth as follows. The bursts have a transmitter.

2 In the particular system with .which this receiver is designed to work the color information is carried by the high frequency portion of the video signals supplied the signal detector 41. This high frequency portion is selected by a band pass supplied to each of three phase detectors 10, 11 and 12. The phase detectors may take manydilerent forms but in general they are modulators in which differentphases of a carrier supplied by an oscillator 13 are modulated by the video signals passed through the filter 9. The output of the oscillator 13 is applied tector 412 via a delay line 14 to a phase detector 11 and via the delay line 14 and another delay line 15 to the The products of modulation prophase detector 10 by the high low frequencies. These low low pass filters 16, 17 and 18 phase detector 10. duced at the outpu-t of the frequencies are selected by respectively and are coupled to the corresponding cathodes 19, 2li-and 21. If the phase detectors 10,v 11 and 12 are balanced against the carrier and against the modulating video signals then the band pass filter 9 and the low pass filters 16, 17 and 18 might be omitted. The important feature is however that the color information carried by the high' frequency video signal is detected by the phase detectors 10, 11 and 12 and applied as low frequency information to the. cathodes 19, 20 and 21.

The highffrequency portion of the video signals was.

originally derived by modulating different phases of a frequency that'isthe same as the output frequency of the .oscillator 13 withv different low frequency color signals.

Therefore, if the delay lines 14 and 15 are -properly ad- 'justed, the phases supplied by the oscillator 13 to the phase detectors 10, 11 and l2 correspondin phase to the phases of this same frequency that was modulated at the Therefore, the modulationsv present in -the different phases of the transmitter are then detected by the phase detectors 10, 11 and 12. This color informaknown and fixed phase and therefore when they are vapplied to two different lphase detectors employed to extract the color information, they themselves will produce voltages fixed ratio if the oscillator to which the phase the proper phase and frequency. v If however this oscillator should drift in phase, the ratio the two phase detectors will having a detectors are coupled has of the voltages supplied by vary from this predetermined amount and this variation n may beernployed to control the phase of theoscillator.l

In the colorreceiver shown in FIGUREl the video 4modulations of themain carrier lare detected by any standard detector land are applied by a delay line 2, an amplifier 3, and a low pass filter 4to the grids of cathode 7 adapted to separately reproduce The proper D C. level for these signals is set by a D.C. restorer 8 of a Inasmuch as the signals are coupled to all three grids they produce brightness variations in the final image and in color variations.

, v the various color information tion that is applied to the cathodes of the kinescopes isv combinedwith the brightness information previouslydescribed so asto produce color signals lof the proper intensity. It can therefore be seen that the proper opera-1 tion of this receiver is only secured when phases of the frequency supplied by the oscillator 13 to the phase de tectors. 10, 11 and 12 coincide with the phases in which signals were modulated at the transmitter. y The manner-in which the present invention fulfills this requirement is as follows. lAs previously stated, the synchronizing information is generally comprised of bursts of a frequency having a fixed phase relationship with respectto the different phases of oscillator frequency that are modulated bythe color information at the transmitter. Therefore each of the phase detectors 10, 11 and 12 will provide a give D C. voltage o'r pulse of a given amplitude in response to each burst of synchronizing signal. The

- amplitude of this pulse will depend uponv the phase relationship between the burst and the output of the oscillatoi- 13 applied to the particular phase detector. In general it can be said that if there is an in-phase relationship that the pulse will be a maximum amplitude if there isl an out-of-phase relationship that the pulses will have a minimum amplitude. Therefore, if the phase relationship between the burst and the phases of the oscillator frequency supplied to the phase detectors 11 and 12 is proper the amplitude of the pulses produced by the detectors 11 and l2 inresponse to the burst of synchronizing energy will have a fixed and known ratio. These pulses are of line frequency if the burst is placed on' the back porch of the horizontalblanking pulse and therefore they pass through thev low pass filters 17 and 18.'

Various means may be provided for separating out the 3,030,436 Patented Apr. l1'1, 1962- filter or afhigh pass filter 9 and directly to the phase de pulses thus produced from the responses of the phase detectors 11 and 12 to the other portions of the video signal train, but in the presentA illustration the pulses thatv of the lowpass filter 18 are selected by a similar type of gate 23. Whatever arrangements are used for the separation i of the pulses produced by detecting the burst in two different phase detectors, these pulses are applied to an amplitude 'detector 24 that'serves toA subtract one from .the other. The detector 24 may be a balanced arrangement orit may be one in which different amplitudes or pulses separated bythe gates 22 and 23 produce zero voltage. The matter of whether the detector 24 should be balanced or unbalanced will be considered in greater detail in connection with FIGURES 2 and 3. The output of the differential detector 24 may be employed in any well known fashion to control the phase of the oscillator 13 in the arrangement shown. However, the output of the detector 24 is applied so as to control the conduction of a reactance tube 26 that' serves to tune the oscillator 13.

The gates 22 and 23 may be rendered capable of passing signals only during the blanking interval in the following manner.- The output of the signal detector 1 is supplied to a sync separator circuit 27 of standard design and the vertical and horizontal sync pulses are supplied by the sync separator to standard sweep circuits 28. If the bursts are placed on the back porch of each line blanking pulse, the gates may be opened inresponse to the y-back pulse appearing in the horizontal sweep circuits. These pulses are supplied to the gates via leads 29 and 30 respectively.

The overall operation of the invention as illustrated in FIGURE 1 may -be more clearly understood after a consideration of the vector diagrams of FIGURES 2 and 3. Let us assume that the vector 31 indicates the phase of the burst of synchronizing energy, and that the vectors 32 and 33 represent the phases of the oscillator 13 that are applied to the phase detectors 11 and V12y respectively. IThe amplitudeof the pulse produced in response to the burst by any phase detector may be determined by projecting the vectors representing the phase of the oscillator 13 supplied to that phase detector upon the vector representing the phase of the incoming burst. Thus if the vectors are 90 out of phase the outputof the phase detectors will be zero. If the vectors become in-phase the amplitude of the pulse may be said to increase in a positive direction, and conversely if lthe vectors become more and more out of phase from ythe 90" position the pulses get larger in a negative direction. In the arrangement of FIGURE 2 it is assumed that the vectors 32 and 33 represent the proper phases of the output ofthe oscillator 13 supplied to the' phase detectors 11 and 12 and that they are symmetrically phased with respect lto the burst. Thus the pulses produced by the phase detectors 11 and 12 are both seen to have an amplitude indicated by the dotted line 34. Therefore, in this particular arrangement, the pulse produced by the phase detectors 11 and 12 in response to the burst are equal in amplitude and the output of the amplitude differential detector 24 may be zero.

However, it is not necessary that the lburst be symmetrically phased with respect to the desired phases supplied by the oscillator 13 to the phase detectors 11 and 12. For example, in FIGURE 3 a `phase of the burst is indicated by a vector 35, the phase of the phase detector 11 is indicated by vector 36 and the desired phase of the phase detector 12 is indicated by the vector 37. The amplitude of the pulse produced in response to the burst at the phase detector 11 will therefore be proportional to the dotted line 38 which represents the projection of the vector 36 onthe vector 35, andthe amplitude of the pulse produced by thephase detector 12 in rev sponse to the pulse 1 indicated by the dotted line 39that is theprojection of the vector 37 on the vector 35. It 1s seen therefore that the pulse provided by the phase detector -11 greatly exceeds the amplitude of the pulsev supplied by the phase detector 12. Therefore, the amplitude differential detector 24 must vbe unbalanced so that the application of these pulses of different amplitudewill produce zero output.v Suppose however that in the arrangement shown in FIGURE 2 the phase ofthe oscl-" lator frequency supplied to the phase detectors 11 and 12 is symmetrical with respect to the burst frequency and that thel oscillator drifts in phase so that the vector 32 assumes the position 32' and that thev vector 33 shifts in the same direction to a position 33'. It cannow be seen that the projection of these two vectors on the vector 31 areunequal, consequently the detected bursts supplied by the phase detector 11 are greater than the detected bursts supplied by the phase detector12. This differential in amplitude between the detected bursts is then applied to the reactance tube 22 so as to speed up the oscillator.

FIGURE 4 illustrates the details of the circuits employed for gating the bursts from the signal train and for producing a phase control voltage wave that is indicative of the difference in amplitude betweenl thev detected bursts. The cathodes of a pair of amplifiers 41I and 42-are connected together by a series of resistors. A

variable contact 43 connects a desired point of one of the resistors to ground. When this contact is setat a neutral position, the resistance in the cathode or path of each of the amplifiers is the same and the gain of the two amplifiers is likewise the same. When, however, it is desired to unbalance the amplifiers 41 and 42 the contact 43 is moved so as to makethe cathode resistance of one amplifier greater than the other. No further detailed .explanation of this is presented as it is felt that the effect of such a contact on the gains of the amplifiers is well understood by those skilled in the art.

The output of the low pass filter 17 is coupled to an amplifier 44 and the output of the low pass filter 18 is coupled to an amplifier 45. The output of the amplifier 44 is coupled to the cathode 20 and the output of the amplifier 45 is coupled to the cathode 21. 'I'hese outputs are also coupled to gating tubes in the form of amplifiers 41 and 42. These tubes are maintained at normal cutoff by the positive voltage placed on their cathodes via the resistors `46 and 47.

The gating tubes 41 and 42 may berendered capable of passing the detected bursts appearing at the output of the low pass filters by applying negative fiyback pulses to the cathodes of the amplifiers 41 and 42. Another way of keying the gating tubes 41 and 42, duringthe burst interval is illustrated in FIGURE 4. The cathodes of the tubes 41 and 42 are coupled via condensers to the upper end of a resistor 48, the lower end of the resistor being connected to ground. The horizontal sync pulses that are separated out in the receiver by 'standard sync separating means are applied to a circuit comprised of a condenser 49 and a resistor 50v so as to produce a wave `51 from a sync pulse 52. The differentiated wave 51 that thus appears across the resistors 50 is coupled to a rectifier 52 via a resistor 53 so that, only the negative portion of the differentiated wave 51 appears across the resistor 48 as such a wave is indicated by thenumeral 54. These negative pulses are applied to the 'cathodes of the gating tubes 41 and 42 and render them conductive. The amount of conduction and therefore the amount of gain produced in response to the pulse 54 is determined by the setting of the contact 43. The pulse produced, in response to the burst by the phase detector 11 appears at the output of the gating tube 41 with a .negative polarity, and the pulse provided by the phase detector 12 in response to the burst appears in negative polarity at the output of the gating tube 42. These pulses are applied push-pull fashion to 'the cathodes of .said higher frequency -said plurality of synchronous detectors, a signal source to I said synchronous vcomprising in combination,

6'1 vand 62 are of equal or opposite polarity so that. the i voltage at the plate of the unilateral device 56 is at ground However.. if the 4pulses supplied by the gating tube 41 have a greater amplitude than those .supplied by the gating tube 42, the unilateral device-S6 conducts more potential.

than the unilateral device 57 and the negative charge built up on the condenser 6l is greater than the negative charge built up on thecondenser 62. As these charges oppose each other, the voltage produced on the condenser 61 more than compensates for the' voltage'produced across the condenser 62 and the plate of the unilateral device `56`becomcs negative with respect to ground.

tubes 42 have a greater am If the pulsessupplied by the gating plitude than the pulses supplied bythe gating tube 41, the

If the output when the outputs of the `vals for opening said gate 'color information recovered from said modulated color subcarrier during said periodically recurring line scanning intervals, a first and second normally-closed gate circuit, each of said gate circuits coupled t'o a different one of said plurality of synchronous only during said periodically recurring line retrace intercircuits during the time intervals that said bursts are applied to said synchronous Vdetectors, an amplitude comparisondevice for subtracting f the. output of one gating device from another to provide a phase-indicative signal indicative of the phase relationship of the phases of said reference signal and said bursts,

- and means forcontrollin'g the frequency ,and phase of the reference signal output of said signal generator responsive to said phase-indicative signal.

3. Apparatus as described in claim 2 wherein said amplitude comparison device is such as to produce zero gate-circuits have a predetermined ratio .diifering from unity.

4. In a color television receiver adapted to receive a color television signal having a higher rfrequency range including a chrominance signal and also bursts of color reverse situation obtains and the plate of the unilateral device 56 becomes positive with respect to ground. It

"- will be understood that other potentialsthan ground may be applied to the plate of the unilateral device 57. `What is claimed is: l. In a color television system wherein the color in-` i formation is conveyed in a higher frequency range ofa television signal by a subcarrier that changes phase and amplitude with respect to a given standard in accordance with-the color information being transmittedand wherein bursts of a wave of the same frequency and having a constant phase relationship to said standard is transmitted in said higher frequency range at line' scanning frequency, a color synchronizing circuit comprising in combination,

a plurality of synchronous detectors, means to apply only range of said television signal to develop different phases of a reference signal having -said subcarrier frequency, means to apply each of said different phases of' said reference 'signal to a different one of said plurality of synchronous said -gating circuits to the output of a different one of detectors, means operating at a line repetition rate for rendering said gating circuits capable .of passing signals only during the times said bursts are applied to said synchronous detectors, means for deriving a control voltage proportional to the algebraic differences between the amplitudes ofthe voltage outputs 'of said gating circuits, and means for controlling the phase of the signal source. with said control voltage.

2. In a color television receiver adapted to receive. a

color television signal having a higher frequency range including both a color su'bcarrier having a given frequency l and subject to modulation in accordance with color information and also bursts of subcarrier frequency at a standard phase of said given frequency, said bursts occurring only during periodically .recurring line retrace intervals and said color subcarrier being subject to modulation in accordance with color information only during periodically recurring line scanning intervals intervening said line retrace intervals, a burst synchronizing circuit a plurality of synchronous detectors each having an output circuit, bandpass filter 'Y means to lter said higher frequency range from said color television signal and 'to apply the color subcarrierand bursts developed therefrom to said plurality of synchronous detectors, a signal generator to develop a reference signal having the frequency of said color subcarrier, means to apply different phases of said reference signal t'o said plurality of synchronous detectors, color information utilization means coupled to the output circuits of said plurality of synchronous detectors and responsive to detectors, a rst and second normally closed gating circuit, means coupling each of phase, said bursts occurring 'curring line retrace intervals a nals related to the phase difference between the phases of said plurality of reference signals and said bursts and to develop during the' recurring periods intervening said recurring line retrace intervals a plurality of detected signals 'representative' of chrominance information, means operatively vcoupled to said signal `detecting means only during said recurring line trace intervals for. subtracting a pair of said detected signals to form a control signal,- and means responsive to said control signal forcontrolling the phases of said plurality of reference signals.

5. Apparatus as described in claim 4 wherein said subtracting means is unbalanced so that the control signal is zero for a predetermined ratio differing from :unity between the outputs of said signal detecting means during the burst interval. 4

. 6.In a color televisionsystem adapted to receive a color television signal lwherein the color information is conveyed by a higher frequency subcarrier that changes with respect toa given standard inv accordance with the color information being transmitted and phase relationship to said standard is transmitted at line scanning frequency, said bursts being transmitted during periodically recurring horizontal blanking intervals, the combination of,` a plurality of synchronous detectors, an oscillator of subcarrier frequency, means to apply differently used phased outputs of said oscilla-tor to said plurality of synchronous detectors, means to apply the subcarrier and burst portion of the received signal to each of said plurality of synchronous detectors to detect the color information represented by the bursts relative to the phasesof each of said outputs, signal sampling means rendered capable of developing sampled outputs only during said recurring horizontal blanking intervals and utilized for sampling the output of each of said plurality of synchronous detectors duringsaid bursts, means for cornparing said sampled outputs during said bursts whereby a control voltage is produced which is proportional to the algebraic difference between the amplitudes of said sampled outputs and means for utilizing said control voltage for controlling the frequency and phase. of said oscillator according to the frequency and phase prescribed by said burst.

7. In a color television system wherein the color indetectors, means effective develop a plurality Y wherein bursts of a wave ofthe same frequency and having a constant 7 formation is conveyed by a subcarrier that changes with respect to a given standard in accordance with the color informationibeing transmitted and wherein bursts of a wave of the same frequency and having a constant phase relationship to said standard is transmitted atv line scanning frequency, said bursts being transmitted during periodical-ly recurring horizontal blanling intervals, the com- Wbination of, a -plurality of synchronous detectors, -an oscillator of subcarrier frequency,` means to apply differently phased outputs of said oscillator to said plurality of synchronous detectors, means to apply the portion of the received signalcomprising said subcarrier and said bursts to the exclusion of a lower frequency portion of said received signal to said plurality of synchronous detectors to detect phase information represented by the bursts in each synchronous detector during said recurring horizontal blanking intervals and to detec'tsaid c olor information during the recurring periods intervening said recurring horizontal blanking interval-s, signal comparison means, means effective only during said 'recurring horizontal blanking intervals for utilizing said signal com- 'parison means for comparing the output of each of said plurality of synchronous detectors during said bursts;

means for deriving a control voltage therefrom which is proportional to the algebraic difference between the arn- I plitudes of said outputs, and means for utilizing said control voltage for controlling the frequency and phase of said oscillator according to the frequency and phase vprescribed by said burst. t

-8. ln a color television receiver adapted to receive a ltelevision signal wherein the amplitude of different phase components of a color subcarrier at a subcarrier frequency form part of a composite signal of video information, said television sign-al also including bursts'of reference phase`information. said .bursts having said subcarrier frequency and occurring during each line retrace interval, the combination of, a plurality of phase de# tectors, an oscillator to develop an output signal at substantially the frequency of said subcarrier, 'means to apply the portion of said television signal comprising said subcarrier and bursts to'the exclusion of a lower frequency portion of said received signal to said phase detectors, means to apply one of different phases of the output signal of said oscillator to each of said phase detectors, a tirstsampling means coupled yto a rst of said plurality of phase detectors and adapted to sample the output of said first phase detector during the recurring line retrace intervals, a second sampling means coupled to a second of said plurality of phase detectors and adapted to sample the output of said second phase detector during the recurring line retract intervals, an amplitude comparing device coupled to said first sampling means and said second sampling means to provide a phase controll signal responsive to the amplitude of the signals provided by said rst sampling means and said second sampling means, said amplitude comparing device having a time constant that is long with respect to a line scanning interval so that said phase control signal substantially retains the value established .during the presence ofeach burst during the following line interval, and means for utilizing 4saidvphase control signal for controlling the frequency and phase of said oscillator.

9. VA control system for a color television receiver comprising: a circuit for supplying a composite video frequency signal comprising during recurring line scanning intervals a color television wave signal amplitude modulated at different phase points by individual ones of signals representative of a plurality'of colors and during intervening line retrace intervals a color synchronizing signal having a phase related to a reference phase of said wave signal; a signal generator for generating a signal ha'rmonically related in frequency to said wave signal and which has a phase which tends to vary from a predeter` mined phase relation with respect to said reference phase;

-a bandpass filter for selectively passing said modulated Wave signal and said color synchronizing to the exclusion of lower frequency components of said composite signal; a control apparatus including a single detection device and a control circuit coupled in cascade, the input circuit of said detection device being coupled to said supply circuit by means of said bandpass filter and being coupled to said generator and. said detection device being responsive jointly during said recurring line" scanning intervals to said wave signal and said generated signal for deriving a signal representative of the modulation cornlponent of said wave signal-at a preselected phase point with Arespect Ato said reference phase and being responsive jointly during said intervening line retrace intervals to said color synchronizing signal and said generated signal to develop an error signal representative of the relative phases of said generated signal and said color synchronizing signal, said control circuit being responsive to said error signal toA derive during said intervening line retrace intervals acontrol etfectrepresentative of the said relative phases; and a control device coupled to said signal generator and said control apparatus and responsive to said control elect for maintaining the phase of said gen-' erated signal substantially at said predetermined phase relation.

'10. A control system for a color television receiver comprising: a circuit for supplying a composite video frequency signal comprising during recurring line scanning intervals a Vcolor television wave signal amplitude modulated at different phase points by individual ones of signalsrepresentative of a plurality of colors and during intervening line retrace intervals a color synchronizing signal having a phase related to a reference phase of said wave signal; a signal generator for generating a signal equal in frequency to said wave signal and which has a phase whichv tends to vary from a predetermined phase relation with respect to said reference phase; a bandpass lter for selectively passing said modulated wave signal and color synchronizing-signal to the exclusion of lower frequency components of said composite signal; a control apparatus-including a single detection device and acontrol circuit coupled'in cascade, the input circuit of saidA detection device being coupled to said supply circuit by means of said bandpass filter and being coupled tosaid generator and said detection device being responsive jointly during said recurring line scanning intervals to said wave signal and saidgenerated signal for deriving a signal representative of the modulation component of Said wave signal at a preselected phase point with respect to said reference phase, and being responsive jointly during said intervening line retrace intervals to said color synchronizing signal and saidgenerated signal to develop an error signal representative of the relative phases of said generated signal and said color synchronizing signal, said control circuit being responsive to said error signal to derive during said intervening line retraceintervals a control effect representative of said relative phases; and a circuit coupled to said generator and said control apparatus and responsive to said control effect for maintaining the phase of said generated signal substantially at said predetermined phase relation.

l1. A color television receiver for utilizing a color television signal which includes color difference components modulated on a subcarrier Wave and which further includes recurring bursts of a signal having a selected phase and frequency with respect to said subcarrier, said bursts recurring at a line repetition rate, said receiver including in combination, apparatus for receiving the color television signal and for deriving the modulated subcarrier and the recurring signal bursts, detector means for recovering the modulation components of the aforesaid subcarrier in response to a demodulating signal having a frequency and phase corresponding to the frequency and phase of the aforesaid subcarrier, a selector network coupled to said apparatus for applying the modulated subcarrier and the recurring signal bursts to 9 said detector means', said detector being subject to ldevelop further signal components corresponding to -tbe ,aforesaid signal bursts with amplitude variations related,

to phase variations between the aforesaid demodulating/ signal and subcarrier, apparatus for developing such a dcrnodulating signal and for supplying the demodulating signal to said detector, means, utilization means for the modulation components and the subcarriercoupled to -said detector means. a control means coupled to said last mentioned apparatus for controlling the frequency and phase of the demodulating signal developed thereby, a

circuit coupled to said detector means and actuated at and phase of the aforesaid subcarrier.

l2. A color television receiver for utilizing a color telen vision signal which includes color difference components modulated on a subcarrier wave and which further includes recurring bursts of a signal having a selected phase and frequency with respect to said subcarrier, said bursts recurring at a line repetition rate, said receiver including in combination, apparatus for receiving the color 'television vsignal and for deriving the modulated subcarrier and recurring signal bursts, detector means for recovering the modulation components of the aforesaid subcarrier in response to a demodulating signal having a frequency and phase corresponding to the frequency and phase of the aforesaid subcarrier, a selector network coupled to said apparatus for applying the modulated subcarrier and the recurring signal bursts to said detector means, said detector being subject to develop further signal cornponents corresponding to the aforesaid signal bursts with amplitude variations related to phase variations between the aforesaid demodulating signal and subcarrier, apparatus for developing such a demodulating signal and for supplying the demodulating signal to said detector means, utilization means for the modulation components of the subcarrier coupled to said detector means and control means for utilizing the aforesaid further signal `components developed by said detector means to control said last-mentioned apparatus and maintain the frequency'and phase of the demodulating signal developed thereby at i bursts to said detector means,

values corresponding to the frequency and phase of the aforesaid subcarrier.

i3. A color television receiver visionlsignal whichlincludes colordifference components modulated on a subcarrier wave, and which further includes horizontal and vertical synchronizing components and recurring bursts of a signal having a selected phase and frequency with respect to said subcarrier, said bursts vhaving a predetermined timing with respect to said synchronizing components and recurring at'the repetition rate of said horizontal synchronizing components, said receiver including in combination, detector means for recovering the modulation components'ofY the aforesaid subcarrier in response. to a demodulating signal having a frequency and phase phase of the aforesaid subcarrier, a selector network responsive to said color television signal for selectively applying the modulated subcarrier and recurring signal said detector being subject to develop further signal components corresponding to the aforesaid signal bursts with lamplitude variations related to phase. variations betweenl the aforesaid demodulating 'signal and subcarrier, apparatus for developing such a demodulating signal and for supplying the demodulating signal to said detector means, a control means coupled to said lastmentioned apparatus for controlling the frequency and phase of the demodulating signal developed thereby, a network for utilizing the aforesaid synchronizing cornl ponents to develop a gating signal having said horizontal repetition rate and recurring at times corresponding to theoccurrence of the aforesaid bursts, a circuit responsive to s aid gating signal for selecting the further'signal components developed by said detector means to produce a control signal having amplitude variations corresponding to amplitude variations of the aforesaid furthery signal components,` and means for applying said control signal to said control means for maintaining the frequency and phase -of the demodulating signal developed by said lastmentioned apparatus at values corresponding to the frequency and phase of the subcarrier.

References Cited in the le of this patent Y UNITED STATES PATENTS for utilizing a color tele-l corresponding to 'the frequency and 

